If I could play devils advocate: I like being able to let people know (in my log, if not others) that their advice has helped.
The rep system I like to use more for when I concur/agree with a post, rather than I have been 'helped' by it. Helpful posts no matter where I read them likewise get the green thumb. Hell, they might get a rep too, if it's really good!
I try not to give unsolicited advice, especially on logs. I don't know if having a helpful is a good or bad things on logs. I doubt it does much to prevent this from happening. To be honest I left it off on a whim.